In order to precisely define the immune response to man, it is necessary to identify the functionally distinct components which contribute to this response. This is a continuation of a proposal which takes advantage of existing methodology for the purification of T, B and Null lymphocytes, and also of recently developed techniques which when used in concert with autoimmune sera or monoclonal antibodies, allow for the identification and differential isolation of several distinct subsets of human T cells. These studies will permit us to 1) functionally characterize each of these distinct subsets, and 2) to examine the effect of each of these T cell subsets on B cell responsiveness, the differentiation of Null cells and perhaps of greater interest, the regulation of other T cell functions. These studies proposed here will facilitate a more precise understanding of the immune response in man and will thereby promote greater insight into immunological abnormalities.